The present invention relates in general to a delay time controlling circuit for use in a group-delay equalizer for R. F. signals, and more particularly, to a delay time controlling circuit capable of minimizing the difference in absolute delay time between two or more broad-band receiver input signals so that it may be adaptable to diversity reception of high speed data signals or super-multiplex telephone signals.
In long distance transmission of microwaves, transmission quality is often deteriorated due to fading. In order to reduce the deterioration of transmission quality caused by the phenomenon, diversity reception has been employed. In a diversity reception it is important to minimize the phase difference between two or more received demodulation signals over a broad frequency band. For instance, in the case of transmitting television signals in an over-the-horizon microwave relay system, certain amount of fluctuations is inevitable in reception time of the respective received waves upon diversity reception because the microwave scattering layer in the atmosphere fluctuates from time to time. Therefore, if the two received waves are simply synthesized, the phase relation therebetween can be such that the received signals may be offset with respect to each other. Therefore, in the case of color television signals, a variation in the intensity and/or phase of the color signals results. Accordingly, a device for equalizing the difference between absolute values of transmission time of the respective diversity signals is desired.
In the conventional absolute delay time controllers, the adjustment is made so that the time difference between the two received signals may be minimized by adjusting the length of a coaxial line or by connecting fixed delay time equalizers in cascade. Every one of these conventional delay time controllers requires mechanical adjustment, which is time consuming and difficult to automate.
It is therefore one object of the present invention to provide a novel delay time controller which can regulate the delay time electronically.
Another object of the present invention is to provide a delay time controller which can easily and automatically bring the delay time difference down to zero.